(a) Technical Field
The present disclosure relates to a method of controlling clutch transfer torque in a hybrid vehicle, in which a clutch friction coefficient is precisely estimated, thereby reducing a shock that can occur in the event of the clutch going on or off.
(b) Background Art
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The hybrid vehicle typically achieve greater fuel economy and lower emission than conventional combustion engine vehicles.
In a parallel hybrid vehicle, as shown in FIG. 1, an engine 10, a motor 20, and an automatic transmission 30 are directly connected on one axis. A clutch 40 is arranged between the engine 10 and the motor 20. Further, in order to operate these components, an integrated starter generator (ISG) 70 is directly connected with a crank pulley of the engine through a belt, and a high-voltage battery 50 is connected with the motor 20 through an inverter 60 so as to be charged or discharged.
As shown in FIG. 2, the clutch 40 is typically a multi-plate clutch, which is operated under constant oil pressure. As shown in FIG. 3, when control current for a clutch hydraulic valve is increased, the oil pressure for operating the clutch is increased, so that the clutch is coupled (or closed).
Methods for controlling a clutch of a hybrid vehicle have been proposed, including a method of learning and correcting the slope of a transfer torque characteristic of a clutch with respect to a stroke of an electric actuator of the clutch, as disclosed in Japanese Patent Application Publication No. 2007-139121, and a method of controlling a clutch on the basis of a clutch control torque characteristic map showing a relation between clutch control oil pressure and clutch transfer torque, and estimating, offsetting and correcting the clutch transfer torque from vehicle acceleration using the map, as disclosed in Japanese Patent Application Publication No. 2006-336854.
However, since the methods do not consider a dead zone and hysteresis, they cannot estimate a friction coefficient “μ” of the clutch precisely. As a result, transmission torque of the clutch cannot be exactly controlled, and thus a shock occurs in the event of the clutch going on or off when the vehicle is converted from its motor-driven mode to engine-driven mode.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.